This invention relates to materials processing. More particulary, it relates to treatment of wafers such as semiconductor wafers with liquid or gaseous fluids.
In the process of fabricating semiconductor wafers, the need to avoid contamination by impurities takes on critical importance. Even in the so-called "clean rooms" of semiconductor fabrication facilities contamination can arise from a variety of sources. Contaminants can originate from human contact, solvent residues and oils from various operations, metals, dust particles, organics and other materials present in processing reagents. Many of the processing steps involved in fabricating a semiconductor wafer require that the wafer be exposed to a fluid, i.e., oxidizing agents, etchants, and washing and rinsing agents. In order to achieve acceptable yields, it is important that each of these steps be carried out in a manner that minimizes the potential for contamination.
Pre-diffusion cleaning is a good example of a step in the process of fabricating semiconductor wafers which must be carefully controlled to avoid contamination. Since the diffusion step in semiconductor processing is intended to "drive-in" desired dopant atoms through high temperature exposure, any contaminants left on the wafer surface after cleaning may also be driven into the wafer and can result in faulty electrical properties.
Pre-diffusion cleaning conventionally is accomplished by loading the wafers into a basket, such as the baskets described in U.S. Pat. Nos. 3,923,156 and 3,926,305, and then immersing the wafers and basket in a series of open sinks or tank baths. Usually the cleaning method involves contacting the wafers first with a strong oxidizing agent, such as sulfuric acid, rinsing with water, then contacting the wafers with an etchant, such as hydrofluoric acid, and then rinsing again. Open baths mounted in countertops pose significant safety problems to technicians who may be exposed to the active reagents or their fumes. Moreover, airborne impurities can and do contaminate the reagents and rinse water, leading to reduced semiconductor yields.
In an effort to avoid open baths, enclosed spray-cleaning devices have been proposed and typically also incorporate spin-drying mechanisms. One example of such a spin-rinser-dryer is disclosed in U.S. Pat. No. 3,760,822. Although this method is an improvement over immersion techniques from the standpoint of safety and airborne contaminant control, the combination of aggressive chemicals and many moving parts results in substantial maintenance problems as well as particulate contamination. Moreover, these designs subject the fragile semiconductor wafers to substantial mechanical stresses.
The need for better systems for treating semiconductor wafers with fluids has become more acute as the circuit element density of solid state devices has increased. Any such system should be capable of treating large numbers of wafers at one time and should be amenable to automated operation. Moving parts and the potential for contamination should be minimized. At the same time, worker exposure to aggressive reagents and/or their fumes should be minimized. A simple, efficient system that permits the safe treatment of semiconductor wafers with fluids in an automated and totally enclosed manner would satisfy a long felt need in the industry. If such a system could improve chip yield by even a fraction of a percent it would greatly benefit the semiconductor manufacturing industry.